The invention relates to a windshield wiper system for a motor vehicle, comprising at least one wiper, a drive, a self-locking device that is active when the drive is in a non-operating state and counteracts a change in position of the wiper, and comprising an electronic control means which actuates the drive and detects the input of position sensor signals of the wiper.
A wiper system of this type comprising means for locking the wiper drive in the non-operating state is already known from DE 103 12 982 A1.
Windshield wiper drive apparatuses in which a rotary movement of a motor which rotates in a prespecified direction is converted into a to-and-fro movement of the windshield wiper by an eccentric mechanism, in particular a crank gear, have long been known. The output shafts of such drives are therefore connected indirectly, via a crank and a thrust linkage, to the wiper shafts to which wiper arms with wiper blades are fixed. The non-uniform transmission ratio of the crank gear, which is minimal in the covered or extended position, produces in these positions, in contrast, a maximum transmission ratio, that is to say one which requires considerable torque, with regard to a rotary movement which originates from the wiper arm and is transmitted to the output shaft. Since the wiper arms in standard wiper drives of this type are arranged in the park or inoperative position in the extended position of the wiper linkage, mechanical self-locking, which is realized by means of the wiper linkage, with regard to a reversed transmission of movement from the wiper arm to the motor is produced on account of these very high transmission ratios within the scope of the customary, indirect transmission of movement without further measures.
When the drive is in the non-operating state, the self-locking device counteracts a change in position of the wiper in the event of a torque which acts on a wiper, which is in the inoperative position, due to external influences. This is desirable since the armature shaft of the wiper motor is not supplied with power in the non-operating state and therefore would rotate freely without adequate self-locking, this producing the risk of the wiper being moved into the wiping area, for example by the head wind.
In more modern wiper systems, drives with reversing electric motors are increasingly being used, in which the motor is controlled in different directions of rotation in accordance with the to-and-fro movement of the wiper. In this case, it is necessary to provide an electronic control means which detects the input of position sensor signals when the wiper is switched on, in order to be able to change over the direction of rotation of the motor at the correct time. Reversing motors of this type permit a more flexible mechanical construction of the wiper system and an enhanced functionality, for example an extended park position. In this case, the wiper is not stored in the lower reverse position, but deeper, that is to say outside the field of view. One problem with this is the slight deviation of the wiper linkage from the extended position, which deviation is associated with the new inoperative position and can lead to excessively weak self-locking of the drive.
A highly desired variant of the reversing drive, the so-called direct wiper drive, is particularly problematical in terms of self-locking. In this case, the output shaft of the worm gear of the drive is connected to a wiper arm directly or via a gear mechanism with a uniform transmission ratio. Since the omission of the crank gear also results in the loss of the self-locking produced by the crank gear, DE 103 12 982 A1 of this generic type proposes providing an additional energy storage means, in particular a helical spring, in the drive in order to produce self-locking in this way.
However, unconventional mechanical self-locking measures such as helical springs or blocking elements are relatively complicated and have to be matched to the respective design of the wiper system. However, complete omission of self-locking measures is not possible either since otherwise, as already explained above, the wiper arm or the wiper arms could move from the park position into the wiping area as a result of misuse or other external influences (for example a car wash).